Snubber seal leakage test circuit

ABSTRACT

The hydraulic system of shock suppressor apparatus for vapor generators utilized in nuclear power plants is provided with integrated fluid circuitry that permits testing for leakage across internal piston seals to be conducted in situ. The fluid circuitry, together with appropriate valving, is operative to hold the piston members of the shock suppressor apparatus in place while testing is conducted and to impart fluid pressures to the system that simulate maximum piston loadings. Sight glass or other detection apparatus is utilized to determine the presence of a leak.

[451 Mar. 5, 1974 1 SNUBBER SEAL LEAKAGE TEST CIRCUIT PrimaryExaminerRichard C. Queisser Assistant ExaminerDaniel M. Yasich [75]Inventor: Daniel Anthony Peel t, South Windsor, Conn.

Attorney, Agent, or Firm.lohn F. Carney [73] Assignee: CombustionEngineering, Inc.,

7 Windsor, Conn.

[57] ABSTRACT The hydraulic system of shock suppressor apparatus forvapor generators utilized in nuclear power plants is [22] Filed: Dec.23, 1971 21 Appl. No.: 211,379

7 provided with integrated fluid circuitry that permits 73/405 73/46testing for leakage across internal piston seals to be conducted insitu. The fluid circuitry, together with appropriate valving, isoperative to hold the piston 29 24 6 m4 1 7 W4 R m m mm GM 7 [51] Int.[58] Field of Search members of the shock suppressor apparatus in placewhile testing is conducted and to impart fluid pres- [56] ReferencesCited sures to the system that simulate maximum piston loadings. Sightglass or other detection apparatus is 'utilized to determine thepresence of a leak.

73/47 5 Claims, 4 Drawing Figures S m m W m m m T u A m m P am S mm Emmmma w T 0 SWDL D W830 664 I999 NHHH 74 511.. .1 2700 www- 3 3 2PAIENTEDMR 5W 3.795.139

SHEH 10F 2 FIG-1 INVENTOR. PAN/EL A PECK BYW M ATT QNEY PATENIEDW W43,795,139

FIG -3 INVENTOR. FIG 4 VAN/EL A- PECK A TTOKNEY SNUBBER SEAL LEAKAGETEST CIRCUIT BACKGROUND OF THE INVENTION Nuclear power plants of thepressurized water type comprise a nuclear reactor and one or more steamgenerators that utilize a primary coolant in the form of pressurizedwater from the reactor to transform a secondary liquid, normally water,into vapor for operating a prime mover, or the like. In the constructionof these plants the vapor generators, which usually comprise verticallyelongated pressure vessels, require support means to prevent the vesselsfrom toppling in the event they are subjected to excessive shockloadings as may be developed by earth termors or as a result ofequipment failure or unusual operational transients. The supportapparatus that is utilized to provide this lateral support must be suchas will permit the vessel to freely undergo thermal growth withoutimparting undue stress to any of its component parts. At the same time,it must be effective to provide rigid lateral support for the vesselwhen a need for such support arises.

Shock suppressor apparatus has been developed that satisfactorilyperforms this function. This apparatus commonly comprises an expandablesupport member including a hydraulic-piston cylinder set and a controlvalve that operates the set such that its effective length can beadjusted in response to thermally induced relative movements that occurbetween the vapor generator and the containment structure within whichit is disposed. The support apparatus can instantaneously be renderedrigid thus to become a load support member when the vessel is subjectedto extraordinary loading, as may occur as a result of earth tremors,equipment failure, or the like. Such apparatus is manufactured and soldby The Grinnell Co., Inc., Providence, Rhode Island under thedesignation Hydraulic Shock and Sway Suppressor," Catalogue ph-69,Drawing No. HE-502l- Periodic testing of the shock suppressor apparatusis required in order to insure that the apparatus will be operative ifand when conditions occur that required it to be placed in service.Current practice involves checking the operability of this apparatus aspart of the procedure followed during normal maintenance shutdowns. Suchchecks include testing for leakage across the internal seals in eachpiston-cylinder set in order to determine whether or not, were leakageto occur, the apparatus would be ineffective to provide lateral loadsupport for the steam generator.

To perform this testing the piston member of the apparatus is normallyheld in a fixed-position and a high pressure fluid simulating maximumdesign load is introduced to the cylinder on one side of the piston.Leakage past the seal is determined by means of a sight glass, or thelike, that is connected to the cylinder on the downstream side of thepiston. In the past, tests of this nature called for physical detachmentof the shock suppressor apparatus from its operative position within theplant and removal to an area where the tests could be conducted. Due tothe size of the components that comprise the shock suppressor apparatus,cranes and other unit-handling apparatus were necessary to effectdetachment of piston-cylinder sets and to transfer them to the testarea. Such procedures are obviously undesirable in that they require theexpenditure of considerable time, effort and expense for theiraccomplishment.

SUMMARY OF THE INVENTION According to the present invention, shocksuppressor apparatus of the described type is provided in its hydraulicsystem with additional fluid circuitry that is operative to efiect insitu testing for fluid leakage across the internal seals of thepiston-cylinder sets utilized in the apparatus. Means are provided forapplying test fluid to the cylinders at a pressure that simulates pistondesign loading. The fluid system is arranged such that the applicationof test fluid occurs simultaneously to two oppositely acting setswhereupon the pistons in each set will be mutually held in a fixedposition relative to the cylinders. As test fluid pressure is increasedto maximum design loading, the occurrence of any leakage across thepiston seals is detected by means of a sight glass that is connected tothe respective cylinderson the downstream side of each piston.

In the described system the circuitry utilized for testing isadvantageously integrated into the hydraulic system of the shocksuppressor apparatus thereby enabling portions of that system to servealso as components of the test circuitry.

For a better understanding of the invention, its operating advantagesand the specific objects obtained by its use, reference should be madeto the accompanying drawings and description which relate to variousembodiments of the invention.

DESCRIPTION OF THE DRAWINGS FIG. I is an elevational view of a nuclearvapor generator organization utilizing a shock suppressor apparatus withwhich the test circuit of the present invention is particularly adaptedfor use.

FIG. 2 is a plan view of the vapor generator organization of FIG. 1.

FIG. 3 is an enlarged sectional view of a pistoncylinder set and acontrol valve that comprises the shock suppressor apparatus.

FIG. 4 is a circuit diagram of the hydraulic system employed to operatethe shock suppressor apparatus of FIG. I and incorporating testcircuitry according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT I In FIGS. 1 and 2 of thedrawings there is shown a nuclear operated vapor generator installation10 embodying the present invention. It comprises a vertically elongated,cylindrical pressure vessel 12 disposed upon the floor 13 of the drywell 14 defined by containment structure 16. The pressure vessel 12contains the operating parts of the vapor generator by means of whichhigh temperature coolant fluid from a nuclear reactor not shown) isplaced in heat exchange relation with a secondary liquid, commonlywater, to transform the same into vapor. Circulation of the coolantfluid between the vapor generator and the reactor is effected by meansof supply and return pipes, 18 and 20 respectively. A vapor outletnozzle 22 is provided at the top of the vessel to conduct vapor producedtherein to a point of use.

The vessel 12 is vertically supported upon a pedestal 24 disposed uponthe floor 13 of the dry well 14. It is connected to the pedestal 24 bymeans of a frustoconical support skirt 26 that is weldedly attached tothe bottom end of the vessel. As shown, the skirt 26 is connected aboutits lower end 38 by appropriate fasteners (not shown) to an upwardlyextending portion 30 of the pedestal 24.

It will be appreciated that, as heat is added or removed .from the vaporgenerator, the vessel 12 will be caused to undergo thermal expansion orcontraction that occurs in both the vertical and lateral directions.Also, the vessel 12 will experience some lateral translatory motion withrespect to the floor 13 of the dry well 14 due to the motion imparted toit as a result of the thermal expansion or contraction of the supplypipe 18.

Therefore, in order to assist in maintaining the vertical alignment ofthe vessel 12 during these periods of thermal growth, a pair of opposedguides may be provided adjacent the upper end of the vessel. in thepreferred embodiment, these guides comprise a pair of keys 32 attachedto the external surface of the vessel at diametrally opposed sidesthereof and spaced guide members 34 secured to the inner surface of thecontainment structure 16 and between which the keys 32 are free toslide. The guides are arranged to permit translatory motion of thevessel 12 in the direction of the axis of the supply pipe 18 but toprevent motion in any other lateral direction.

The means provided to laterally support the vapor generator vessel 12against undue shock loading is indicated generally as the shocksuppressor apparatus 36. As best shown in FIG. 2, two such assembliesare utilized in the described organization each being disposed onopposite sides of vessel 12. Each shock suppressor apparatus 36comprises a pair of oppositely spaced cylinders 38 whose closed ends arepivotally attached to the adjacent wall of the containment structure 16by means of an appropriate connection which may include the illustratedclevis 40 and pin 42. The cylinders 38 each contain a reciprocatablepiston 44 having an axially extending piston rod 46. The cylinders 38and connected pistons 44 are oppositely spaced in mutual horizontalalignment and the opposed piston rods 46 are both attached to theexternal surface of the vapor generator l2, connecting to a common pivotpin 48, or the like, that extend radially from the external surface ofthe vessel. As a result of the described structure the opposed pistons44 in each apparatus 36, being interconnected, are caused to translatein unison.

Seal rings 49 are provided about the pistons 44 to maintain an effectivefluid seal within the cylinder between the upstream and downstream sidesof the piston. The seal rings 49 may be formed of resilient O- rings andare mounted in circumferential grooves (not shown) provided in theexternal surface of the pistons. The seal is effected by the engagementof the respective seal rings 49 with the internal surfaces of theassociated cylinders 38.

The shock suppressor apparatus 36 are arranged to permit unrestrictedrelative movement between the vessel 12 and the containment structure 16when the vessel undergoes normal thermally-induced movements duringvarious phases of plant operation. Upon the occurrence of a shock loadupon the system, however, means are provided to render the shocksuppressor apparatus 36 rigid such that they are operative to supportthe vessel 12 against the lateral forces generated by the shock loading.The assemblies 36 are caused to operate in the described manner as aresult of the operation of control valves, indicated as 50, that areassociated with each of the piston-cylinder sets. One such control valve50 is shown schematically in FIG. 3 in operative position with respectto its associated piston-cylinder set. The valve comprises a body 52having a through passage 54 terminating at each end in enlarged diameterchambers 56 and 58. The chambers 56 and 58 connect with the cylinder 38on the respective sides of the piston 44 by means of hydraulic lines 60and 62 respectively. Isolation valves 63 are dis posed in each of thelines 60 and serve to isolate the control valve 50 during conduct of thetest for piston seal leakage as described hereinafter. The chambers 56and 58 each contain a poppet 64 that is biased to an open position bymeans of a spring'66. The characteristics of the springs 66 are suchthat the respective poppets 64 will be held open during periods ofnormal translatory activity of the vapor generator vessel 12.

During these periods, movements of the respective pis-.

tons 44 caused by thermal growth or translation of the vessl vessel uponthe floor 13 of the dry well 14 will be imparted to the pistons throughthe pins 48. Such movement is permitted due to the substantiallyunrestricted flow of hydraulic fluid from one side of the piston to theother through lines 60 and 62 and the open poppets 64 in the controlvalve 50. It will be appreciated that, during these periods theinterconnected piston pairs in each apparatus 36 will be caused totranslate unrestrictedly in unison within their respective cylinders 38.

To accommodate the difference in cylinder volume on the respective sidesof the pistons 44 due to the presence of the piston rods 46, the controlvalves 50 are provided with bleeder ports 67 which are connected bymeans of lines 68 to fluid reservoir 70 (FIG. 4). A valve 72 is providedin line 68 downstream of the reservoir 70 and forms part of the testcircuit of the present application. Its function is to isolate thereservoir during periods of testing.

FIG. 4 illustrates, in schematic form, the hydraulic system utilized inthe operation of the described shock suppressor apparatus 36. Asdisclosed hereinabove, the operation of the assemblies 36 is governed bythe controlled transfer of operation fluid from one cylinder chamber tothe other through lines 60 and 62 and the respective control valves 50.The system additionally incorporates a fluid circuit, indicated as line74, that serves to establish fluid communication between the left handchambers of all of the cylinders 38 as viewed in FIG. 4. A similarcircuit, indicated as 76, connects the right hand chambers of thecylinders. The fluid circuits 74 and 76 each serve to assist inproducing the substantially simultaneous operation of the poppets 64 inthe respective control valves 50 in the event of undue shock loadings onthe vessel. Thus, the circuit formed by lines 74 is operative when theapparatus is subjected to a shock loading to transfer fluid from theleft chambers of the cylinders 38 when one or more of the poppets 64 intheir associated control valve or valves is slow to close therebypermitting continued movement of the vessel 12 and therefore translationof the piston pairs toward the left. The fluid displaced through lines74 is distributed to all of the left hand chambers thereby increasingfluid flow through the affected control valve or valves to induceclosure of the slow closing poppets.

When movement of the vessel 12, and thereby the connected piston pairsis toward the right the circuit formed by lines 76 is effective toperform the same function with respect to the fluid from the right handchambers of the respective cylinders 38.

In accordance with the present invention additional circuitry, andappropriate valving, is attached to the hydraulic system that iseffective to enable the testing for leakage across the piston seals 49without the need for dismantling the assembly components. This circuitryincludes lines 78 containing operating valve 80 that communicatesbetween a source of high pressure test fluid ideally maintained at about3,000 psi and that portion of the circuit formed by lines 76 thatcommunicates with the right hand chambers of those cylinders 38 locatedon the right side of the arrangement as viewed in FIG. 4. Another line,indicated as 82, is connected between line 76 upstream of shutoff valve84 and that part of line 74 that communicates with the left handchambers of the cylinders 38 located on the left side of thearrangement. Test fluid is thereby capable of being applied to therespective cylinders 38 in each assembly 36, as shown by the solidarrows in the drawing in a manner as will apply opposite counteractingforces on the respective pistons 40 of each piston pair thereby beingeffective to maintain them in equilibrium and thus rigidly heldstationary in their associated cylinders.

Sight glasses 86 are utilized to detect the presence of leakage fluidpast any of the fluid seals. These are connected in the system to thoseparts of lines 74 and 76 that communicate with respective cylinders 38on the downstream sides of the respective pistons 40. Connection of thesight glasses 86 to the system can be conveniently effected byconnecting the same to the lines 74 and 76, as by means of lines 88containing sight glass valves 90. The upper ends of the sight glasses isin communication with the atmosphere to permit leakage flow thereinto.

The operation of the above-described vapor generator shock supportarrangement is as follows. During periods that the plant is in operationand the assemblies 36 are operative to provide their support function,valves 63, 72, 77, 84 and 92 are maintained in an open condition andvalves 80 and 90 are closed. The entire system is filled with operatingliquid. As motion occurs in the vapor generator vessel 12 due to thermalgrowth and translatory motion of the vessel upon the floor 13 of the drywell 14 the piston pairs in the shock suppressor assemblies 36 arecaused to move within the respective cylinders 38 in response to thevessel movement and their connection to the vessel at pins 48. Dependingupon the direction of movement of the vessel operating liquid will betransferred through the control valve 50 to opposite sides of thepistons 44 either from lines 60 to 62 or vice versa. Since both poppets64 in each control valve 50 are open movement of the piston pairs willbe substantially unrestricted. As described above the liquid volumeimbalance caused by the piston rods 46 is accommodated by a flow ofliquid through lines 68 to or from reservoir 70.

In the event of excessive transverse loading on the vapor generator, asfor example, loading caused by an earth tremor, the excessive rate offlow of operating fluid caused by movement of the piston pair due totheir connection with the vessel 12 will cause one of the poppets 64 ineach control valve 50 to rapidly close. If

the affected poppets 64 in all control valves close simultaneously aswill ideally occur the system is immediately imparted with load supportcapabilities opposing the developed forces due to the incompressibilityof the hydraulic system. If, however, one or more of the poppets 64closes more slowly than the others thereby permitting the vessel 12 tocontinue its shock induced movement the fluid displaced by those pistonswhose associated poppets have closed is distributed to the remainingcylinders 38 through lines 74 or 76 depending on the direction ofmovement of the piston couples. The increased flow of fluid to theaffected control valves 50 is effective to accelerate closure of thestillopened poppet or poppets 64 to prevent further movement in thesystem.

When it is desired to test for leakage past the seal rings 49 which isimportant to determine the operability of the shock suppressorassemblies 36 the normally open valves 63, 72, 77 and 84 are closed andvalves 90 opened. Valves 92 are also initially retained in their openposition. To conductthe test, valve 80 is opened to apply test pressureto the system as indicated by the solid arrows in FIG. 4. As the systemis viewed in FIG. 4 of the drawing the respective cylinders 38 will bepressurized on opposite sides of the piston couples, the

right chamber of the right hand cylinders being placed I incommunication with the source of high pressure test fluid through linesand 76 and the left chambers of the left hand cylinders being similarlyconnected through lines 60, 74 and 82. With test fluid being oppositelyapplied to the piston couples the pistons are held in place. Any leakageof test fluid that might occur past the seal rings 49 is detectable inthe sight glasses 86 that communicate with the respective cylindersthrough lines 62, 74 and 62, 76. The flow of leakage fluid is indicatedin FIG. 4 by the broken lines.

Isolation valves 92 are disposed in lines 74 and 76 respectively for thepurpose of isolating the upstream one in each cylinder pair thatconnects with the respective sight glasses 86. By means of the isolationvalves 92, therefore, one of the two cylinders connected to each sightglass can be isolated such that a determination can be made as to whichof the two cylinders 38 is leaking when the presence of leakage isdetected in the sight glass.

By means of the described apparatus, therefore, there is provided asimple yet effective arrangement for testing the operability of nuclearvapor generator shock suppressor apparatus. The arrangement isparticularly advantageous in that it enables testing to be conductedwithout the need of dismantling the apparatus and transferring it to anarea where testing can be accomplished. Additionally, the describedadvantages are achieved by utilizing much of the fluid circuitry in thehydraulic system of the shock suppressor apparatus with only a minimumof additional equipment being required.

It will be understood that various changes in the details, materials andarrangements of parts which have been herein described andillustrated inorder to explain the nature of the invention, may be made by thoseskilled in the art within the principle and scope of the invention asexpressed in the appended claims.

What is claimed is:

1. In combination with shock suppressor apparatus for supporting anupstanding body subjected to relative movement with respect to adjacentstationary base structure, said shock suppressor apparatus including atleast one pair of oppositely acting piston-cylinder sets having twoaligned, oppositely spaced cylinders attached to said base structure, amovable piston containing a piston seal operative in each of saidcylinders,said

pistons having piston rods that are connected to said body and mutuallyinterconnected for simultaneous movement of the piston-couple withrespect to said cylinders, and fluid system means for supplyingoperating cylinders on the sides of the respective pistons oppositc tothat to which said fluid is admitted.

2. Apparatus as recited in claim 1 in which said leakage detection meansincludes a sight glass.

3. Apparatus as recited in claim 2 including means for connecting saidpiston-cylinder sets to said sight glass in series and further includingvalve means in said fluid system means for isolating a selected one ofsaid sets from said sight glass.

4. Apparatus as recited in claim 1 wherein the test -fluid applied tosaid system emanates from a source at a greater pressure than thepressure in the fluid system of said shock suppressor apparatus andincluding valve means in said fluid system means for selectivelyisolating said source from said system during normal operation of saidsystem.

5. Apparatus as recited in claim 4 wherein the pressure of said testfluid is maintained at a level to simulate maximum system designloadings. I

1. In combination with shock suppressor apparatus for supporting anupstanding body subjected to relative movement with respect to adjacentstationary base structure, said shock suppressor apparatus including atleast one pair of oppositely acting piston-cylinder sets having twoaligned, oppositely spaced cylinders attached to said base structure, amovable piston containing a piston seal operative in each of saidcylinders, said pistons having piston rods that are connected to saidbody and mutually interconnected for simultaneous movement of thepiston-couple with respect to said cylinders, and fluid system means forsupplying operating fluid to the two cylinders in said sets, includingmeans for testing for leakage across said piston seals, in situcomprising: a. means for simultaneously supplying test fluid to bothcylinders in a set, said fluid being admitted to said cylinders on thesides of the respective pistons to generate oppositely acting forces onthe interconnected pair of pistons; b. leakage detecting means; and c.means connecting said leakage detecting means to said cylinders, saidmeans communicating with said cylinders on the sides of the respectivepistons opposite to that to which said fluid is admitted.
 2. Apparatusas recited in claim 1 in which said leakage detection means includes asight glass.
 3. Apparatus as recited in claim 2 including means forconnecting said piston-cylinder sets to said sight glass in series andfurther including valve means in said fluid system means for isolating aselected one of said sets from said sight glass.
 4. Apparatus as recitedin claim 1 wherein the test fluid applied to said system emanates from asource at a greater pressure than the pressure in the fluid system ofsaid shock suppressor apparatus and including valve means in said fluidsystem means for selectively isolating said source from said systemduring normal operation of said system.
 5. Apparatus as recited in claim4 wherein the pressure of said test fluid is maintained at a level tosimulate maximum system design loadings.